Method of producing sulfur tetrafluoride from uranium tetrafluoride

ABSTRACT

A method for converting depleted uranium tetrafluoride (UF 4 ) to triuranium octaoxide (U 3 O 8 ), and producing sulfur tetrafluoride, using a two step process. The first step uses heat and a mixture of the uranium tetrafluoride and an alkaline compound, either an alkaline oxide or an alkaline hydroxide, to produce U 3 O 8  and a water-soluble metal halide. The second step uses heat, sulfur and a halogen to produce sulfur tetrafluoride and triuranium octaoxide.

PRIORITY/CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/279,999 filed Oct. 29, 2009, the disclosure of which is incorporatedby reference.

TECHNICAL FIELD

The presently disclosed and claimed inventive concept(s) generallyrelates to a method for making triuranium octaoxide and moreparticularly to a method of making uranium-free sulfur tetrafluoride,and triuranium octaoxide from uranium tetrafluoride.

BACKGROUND

The current state-of-the-art in depleted uranium processing requiresthat DUF₆ tailings be converted into DUF₄ (depleted uraniumtetrafluoride), which can be processed into metallic inorganic fluoridegases, like GeF₄, SiF₄, and BF₃. Pearlhill Technologies has just provedit is feasible to develop nonmetallic inorganic fluorides from uraniumtetrafluoride (NIFUT) to produce sulfur tetrafluoride (SF₄) gas andtriuranium octaoxide (U₃O₈) from depleted UF₄. Producing SF₄ opens thedoor to a whole range of metallic inorganic fluoride gases withestablished commercial markets. This project will contribute to uraniumtailing management in the Excess Uranium Inventory Management Plan ofthe United States Department of Energy, by achieving viable large scalefluorine recovery for civilian market.

Currently, conversion processes involve either (i) hydrolysis of DUF₆ toproduce U₃O₈, along with anhydrous hydrogen fluoride (HF); or (ii) usingthe fluorine extraction process (FEP) to produce commercially valuablemetal fluorides, such as BF₃, GeF₄, SiF₄, and U₃O₈. This technology (i)is economically unviable; and the FEP technology for production ofmetallic fluorides, such as BF₃, GeF₄, and SiF₄, appears to be viablefor production of very expensive high purity gas product grades that arepriced to pay for the high cost of production. While the FEP isprofitable for production of expensive, limited-volume specialtyproducts like GeF₄, it is still to be proven viable for bulk gases BF₃,and SiF₄, respectively.

Meanwhile, DOE has 700,000 metric tons of UF₆ that can be recovered intouseful marketable fluorinated products. United States EnrichmentCorporation (USEC), Louisiana Energy Services (LES), AREVA Inc., andGeneral Electric (GE) have all either announced plans to build, or arebuilding new nuclear fuel enrichment facilities in the United States.When these facilities are completed, at their initial stated capacity,they will produce approximately 60 million pounds of DUF₆ tails eachyear. DUF₆ cannot be disposed of directly, but must be converted intodisposable waste forms. There are very few facilities in the U.S. todaythat can convert depleted DUF₆ tails. This patent presents the mosteffective and economically viable alternative technology for fluoriderecovery from UF₆.

SUMMARY

The innovation is an energy efficient, two-step process for productionof uranium free SF₄ from UF₄, called nonmetallic inorganic fluoride fromuranium tetrafluoride (NIFUT) technology. The uranium byproduct of theprocesses in this technology is pure U₃O₈ and a water-soluble metalhalide. It produces uranium-free SF₄ gas from a room temperaturereaction that can be operated for large scale production of commerciallyvaluable SF₄, at a competitive cost with the alternative currentindustrial. NIFUT technology can produce high quality SF₄, to be used bymanufacturers of active pharmaceutical ingredients (APIs),agrochemicals, inorganic chemicals, and fluoropolymers.

The invention is a method for converting depleted uranium tetrafluoride(UF₄) to uranium free sulfur tetrafluoride (SF₄) and triuraniumoctaoxide (U₃O₈). This method starts with the first step which isheating a mixture of uranium tetrafluoride and an alkaline compound.These two reagents can be heated at various temperatures, with 350° C.to 650° C. being a typical range. The two reagents are heated in areaction chamber for 60-240 minutes. The reaction chamber is flushedwith dry air from a gas reservoir. Off gases from the reaction of thefirst step occur, and are passed through a filter to prevent particulateuranium from escaping from the reaction chamber.

The next step is allowing a mixture of the uranium containing productfrom the first step, combined with sulfur (S) and a halogen to be placein the same reactor. This process is operated at a temperature ofapproximately 25-80° C., for varying times including 96 hours to 120hours. The heating of the uranium containing product along with sulfur(S) and a halogen produces sulfur tetrafluoride (SF₄) gas, and solidbyproducts of a metal halide salt and U₃O₈ has to be at temperaturesbelow 400° C. that is favorable for re-fluorination of U₃O₈ to produceUF₆.

The reactant defined above as an alkaline compound can take the form ofeither an alkaline oxide or an alkaline hydroxide. The alkaline oxideswhich have proven favorable for this reaction include cesium oxide,calcium oxide, and potassium oxide. An alkaline oxide for use in thereaction above can be selected from the group consisting of calciumoxide, cesium oxide, and potassium oxide. The preferred halogen ischlorine, although bromine is also a suitable and a preferred halogen.

One version of the method described above utilizes cesium fluoride (CsF)to combine with sulfur, and a halogen reagent to produce tetrafluoride(SF₄) in the second step. The second step of this version of thereaction could utilize bromine or chlorine, with chlorine beingpreferred. This version of the reaction can be conducted at 25-80° C.for 96-120 hours.

Another embodiment of the method of the invention utilizes cesiumhydroxide and uranium tetrafluoride in a reaction chamber at 350-650°C., for 60-240 minutes in the first step. The second step of thisversion of the reaction preferably utilizes chlorine with bromine alsobeing suitable as a halogen.

Among the alkaline hydroxides which may be utilized for step one of thismethod are potassium hydroxide and cesium hydroxide.

Another embodiment of the method of the invention utilizes cesiumcarbonate and uranium tetrafluoride in a reaction chamber at 350-650°C., for 60-240 minutes in the first step. The second step of thisversion of the reaction preferably utilizes chlorine with bromine alsobeing suitable as a halogen.

Among the alkaline carbonates which may be utilized for step one of thismethod are potassium carbonate and cesium carbonate.

The method can be operated using the reagents potassium hydroxide andchlorine, potassium hydroxide and bromine, cesium hydroxide andchlorine, or cesium hydroxide and bromine.

Similarly, sodium oxide, potassium oxide, cesium oxide potassiumcarbonate, and cesium carbonate can be utilized with either chlorine orbromine.

The method can be conducted at various temperatures and times including400-600° F. Step two of the method can also be conducted at 80° C. orless for less than 10 hours utilizing bromine as the halogen.

The atmosphere in which the heating step of step one is conducted wouldtypically be dry air, which flushes the reaction chamber and causes offgases to go to a KOH scrubber. Step two of the method utilizes acryogenic condenser to collect the SF₄ gas.

The purpose of the Abstract is to enable the public, and especially thescientists, engineers, and practitioners in the art who are not familiarwith patent or legal terms or phraseology, to determine quickly from acursory inspection, the nature and essence of the technical disclosureof the application. The Abstract is neither intended to define theinventive concept(s) of the application, which is measured by theclaims, nor is it intended to be limiting as to the scope of theinventive concept(s) in any way.

Still other features and advantages of the presently disclosed andclaimed inventive concept(s) will become readily apparent to thoseskilled in this art from the following detailed description describingpreferred embodiments of the inventive concept(s), simply by way ofillustration of the best mode contemplated by carrying out the inventiveconcept(s). As will be realized, the inventive concept(s) is capable ofmodification in various obvious respects without departing from theinventive concept(s). Accordingly, the drawings and description of thepreferred embodiments are to be regarded as illustrative in nature, andnot as restrictive in nature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of NIFUT production of nonmetallic fluoride gasesfrom DUF₄ and other available alternative technologies for fluoriderecovery from DUF₄.

FIG. 2 shows uses of SF₄ combined with carboxylic acids inpharmaceuticals and agrochemicals.

FIG. 3 shows uses of SF₄ combined with ketones, aldehydes, or alcoholsin pharmaceuticals and agrochemicals.

FIG. 4 shows the presence of U₃O₈ in the X-Ray diffraction (XRD) patternof a sample after stoichiometric mixture of Na₂O—Na₂O₂ (80:20) and UF₄were heated at 600° C. for one hour.

FIG. 5 shows the presence of U₃O₈ in the X-Ray diffraction (XRD) patternof a sample after stoichiometric mixture of CaO and UF₄ were heated at600° C. for one hour.

FIG. 6 shows the presence of U₃O₈ in the X-Ray diffraction (XRD) patternof a sample after stoichiometric mixture of MgO and UF₄ were heated at600° C. for one hour.

FIG. 7 shows XRD pattern for UF₄ as reference for identification ofuranium by products of steps 1 and 2.

FIG. 8 shows XRD pattern for U₃O₈ as reference for identification ofuranium byproducts of steps 1 and 2.

FIG. 9 shows XRD pattern for UO₃ as reference for identification ofuranium byproducts of steps 1 and 2.

FIG. 10 shows XRD pattern for UO₂ as reference for identification ofuranium byproducts of steps 1 and 2.

FIG. 11 shows a summary of logarithms of equilibrium constants listed inTable 6.

FIG. 12 shows a summary of logarithms of equilibrium constants listed inTable 6.

FIG. 13 is a diagram of the laboratory scale apparatus for SF₄production for step one.

FIG. 14 is a diagram of the laboratory scale apparatus for SF₄production, for step two.

FIG. 15 is a graph of FTIR absorbance spectrum of 30% SF₄.

DETAILED DESCRIPTION OF THE PREFERRED AND EXEMPLARY EMBODIMENTS

While the presently disclosed inventive concept(s) is susceptible ofvarious modifications and alternative constructions, certain illustratedembodiments thereof have been shown in the drawings and will bedescribed below in detail. It should be understood, however, that thereis no intention to limit the inventive concept(s) to the specific formdisclosed, but, on the contrary, the presently disclosed and claimedinventive concept(s) is to cover all modifications, alternativeconstructions, and equivalents falling within the spirit and scope ofthe inventive concept(s) as defined in the claims

A preferred embodiment of the method is the production of sulfurtetrafluoride (SF₄) from uranium tetrafluoride by a two-step process.This process results in nonmetallic inorganic fluorides from uraniumtetrafluoride (NIFUT) to produce sulfur tetrafluoride (SF₄) gas andtriuranium octaoxide (U₃O₈) from depleted UF₄. This process is shown inFIG. 1. The production of sulfur tetrafluoride is commercially valuablebecause when SF₄ is combined with carboxylic acids, many products usefulin pharmaceuticals and agrochemicals can be made, as shown in FIG. 2.When SF₄ is combined with ketones, aldehydes, or alcohols, many productsuseful in pharmaceuticals and agrochemicals can be made, as shown inFIG. 3.

Step One: The first step of this particular embodiment of the method isto combine a mixture of uranium tetrafluoride (UF₄, a green solid) andan alkaline compound, such as sodium oxide or cesium oxide (Na₂O—Na₂O₂or Cs₂O, white solids). An alkaline oxide, alkaline carbonate, or analkaline hydroxide can be used, such as sodium oxide, sodium hydroxide,cesium carbonate, cesium oxide, cesium hydroxide, potassium oxide,potassium carbonate, or potassium hydroxide. The next step is heating to400° C. with sufficient air present, for 15 hours. Heating to 600° C.produced complete conversion of UF₄ within 4 hr. The reaction at 400° C.achieves about 70% conversion after 15 h. The products of the reactionare, and will have, an orange-grey and grey color, respectively. Theuranium byproduct of the processes in this technology is pure U₃O₈ and awater-soluble metal halide.

The quantities of uranium tetrafluoride and alkali metal oxide, as anexample, can be in the range of 314 g of uranium tetrafluoride to massequivalent of 1 mole of alkali metal oxide

In the preferred embodiment, heat is applied to the stainless steelreactor or other suitable container using a Lindberg Blue heater, a Parrheater, or other suitable heating apparatus and methods can be used.

An alternative preferred embodiment involves the reaction of uraniumtetrafluoride and cesium hydroxide (CsOH) or potassium hydroxide (KOH)at 450° C. in the presence of air, and over 12 h, resulted in theproduction of corresponding anhydrous fluoride salts, i.e. CsF and KF,and U₃O₈ as the uranium byproduct

A preferred production apparatus for carrying out the method 10 is shownin FIGS. 13 and 14, and would be scaled up for large scale production,with equivalent equipment to the equipment shown in the laboratory scaleembodiment. Shown in FIG. 13 is a 304 or 316 L stainless steel cylinder14 which serves as a crucible or reaction vessel, and a heat source 16.A thermocouple 18 is present to monitor the temperature of the reactionchamber 14.

Attached to the stainless steel cylinder 14 is a T coupling, with the Tcoupling in the laboratory scale version being a 1 inch stainlessfitting with a 1 inch top opening 22, and a 1 inch side opening 24.Inserted into the top opening 22 is a gas line 26, in this case made ofstainless steel, although Hastelloy C, Monel, or other suitable materialcould be utilized for the gas line 26.

The gas line 26 extends to a dry air source 28, with an inline valve 30,pressure regulator 32, and mass flow meter 34 being present on the gasline 26. The dry air source supplies air to flush the gases from thereaction chamber 14.

Attached to the side opening 24 is a 1 inch outflow line 36, with agauge 38, a valve 40, and a filter 42. The material of the outflow lineis preferably stainless steel in the laboratory scale setup, but couldalso be Teflon, Hastelloy C, or Monel, or any suitable material in alarger production model. The purpose of the filter 42 is to prevent anyparticulate uranium from leaving the reaction vessel 14, and a suitablefilter is a 0.3 micrometer Pall's Gaskleen V filter, although othersuitable filters may be used.

Gas passing through the filter 42 is routed through the online gas cell44 which is located in analytical instrumentation 46 to test for thecomposition of volatile effluents. Effluents pass through the gas cell44, to either a cryogenically cooled condenser or a KOH scrubber 48, andare vented from the KOH scrubber 48 through a vent 50. In the laboratoryscale setup, the preferred analytical instrumentation is a FourierTransform Infrared (FTIR) spectrometer, or a gas chromatograph (GC). TheKOH scrubber is approximately 5 L in volume, and contains 1-5 M KOH, andwould be scaled up for larger production.

The reactivity's of MgO, CaO, or Na₂O with UF₄ were determined over awide range of temperature. The process involved addition ofstoichiometric quantities of each oxide with UF₄, and heating to 600° C.for 30 minutes. The physical look of the products vs. starting materialswere photographed, showing color change from white (metal oxide, MO_(x))or green (UF₄) to grey final color. In the case of 80:20 Na₂O—Na₂O₂,there was a separate yellow-red colored product that stayed on top ofthe grey powder. Powder X-Ray diffraction (XRD) data confirm that thereaction of UF₄ was rapid and complete, producing U₃O₈, and therespective metal fluorides.

However, the effort to produce SF₄ from the reaction of (i) NaF/S/Br₂,(ii) MgF₂/S/Br₂, or (iii) CaF₂/S/Br₂ at room temperature wasunsuccessful. The computerized study evaluation of thermodynamicfeasibility of conversion of the metal fluorides to SF₄ was undertakenusing the HSC 7.0 software. The results are summarized in Tables 1 to 7as in FIGS. 11 and 12. The results showed that the best candidates wereCsF and KF.

The most practicable commercial approach to producing KF or CsF from UF₄involved dehydration of the mixture of the metal hydroxide and UF₄ at600° C., with flowing air. The only byproducts are dry U₃O₈ and therespective metal fluoride (MF_(n)). When this product has beensufficiently dehydrated, the MF_(n) represents the best chemical reagentfor production SF₄, in the presence of U₃O₈; and resulting in <10,000ppm of SOF₂ and HF.4M-OH+3UF₄+O₂→4MF_(n)+U₃O₈+6H₂OU₃O₈+4MF_(n)+S+2Cl₂→SF₄(g)+4MCl+U₃O₈

Early investigation of this approach produced encouraging results. Whenthe mixtures of (i) CsF/S/Cl₂, ad (ii) CsF/S/Br₂ were allowed to sit atroom temperature, 75%, and 60% conversion of S/Cl₂ to SF₄ had occurredwithin 72 h. Although, these two processes resulted in the production ofSF₄, the byproduct from CsF/S/Br₂ was a messy brown viscous liquid! Thiswill complicate the clean up of U₃O₈, a make the process anuncomfortable task because of the presence of residual bromine. On theother hand, the gas-solid process of CsF/S/Cl₂ produced SF₄ and lightyellow CaCl/CsF solid mixture, which changed to white on standing in thehood. Thus, on the basis of the kinetic advantages, better thermodynamicfeasibility, and less complex byproducts stream, the CsF/S/Cl₂ processwas selected for study of the U₃O₈—CsF/S/Cl₂ and U₃O₈—KF/S/Cl₂ systems.The progress of the reaction can be monitored by Fourier Transforminfrared (FTIR) spectrometer. The yield of the process was studied byrecording the pressure in batch processes at (a) RT; and (b) 80° C./8 h.The general balanced equation shows that the product (SF₄) pressure willbe half as much as the reagent gas (Cl₂) pressure.

A successful process must prevent the conversion of U₃O₈ to UF₆. SF₄reacts with UO₂, UO₃, and U₃O₈ to produce UF₆ at 100, 300 and 400° C.,respectively. Therefore, the ideal commercial process must operate at orbelow 100° C. The KOH/UF₄, CsOH.H₂O/UF₄, and the resultant U₃O₈—KF/S/Cl₂and U₃O₈—CsF/S/Cl₂ processes were assembled according to the set up inFIGS. 13 and 14. Kinetic information was obtained by recording changesin pressure periodically. The reaction of cesium hydroxide (CsOH) andUF₄ to produce CsF/U₃O₈ is thermodynamically favored (see Table 1), andwas carried out at 600° C. to ensure complete dehydration of CsFproduced.

FIG. 4 shows the presence of U₃O₈ in the X-Ray diffraction (XRD) patternof a sample “J” after step 1 of the method, after stoichiometric mixtureof Na₂O—Na₂O₂ (80:20) and UF₄ were heated at 600° C. for one hour.

FIG. 5 shows the presence of U₃O₈ in the X-Ray diffraction (XRD) patternof a sample “K” after step 1 of the method, after stoichiometric mixtureof CaO and UF₄ were heated at 600° C. for one hour.

FIG. 6 shows the presence of U₃O₈ in the X-Ray diffraction (XRD) patternof a sample “L” after step 1 of the method, after stoichiometric mixtureof MgO and UF₄ were heated at 600° C. for one hour.

FIG. 7 shows XRD pattern for UF₄ as reference for identification ofuranium byproducts of steps 1 and 2.

FIG. 8 shows XRD pattern for U₃O₈ as reference for identification ofuranium byproducts of steps 1 and 2.

FIG. 9 shows XRD pattern for UO₃ as reference for identification ofuranium byproducts of steps 1 and 2.

FIG. 10 shows XRD pattern for UO₂ as reference for identification ofuranium byproducts of steps 1 and 2.

Step Two: The second step of the two-step process involves addingpowdered sulfur (S) and a halogen, such as bromine (Br₂) or chlorine(Cl₂), to the mixture of U₃O₈—CsF or U₃O₈—KF (from step 1); and stirringthis in a reactor at room temperature for 3 hrs to 200 hrs, with 120hours being typical, to produce sulfur tetrafluoride (SF₄) gas inquantitative conversion, with the solid byproducts being alkalinehalide, and U₃O₈.

Stoichiometric quantities of sulfur (S) and a halogen such as bromine(Br₂) or chlorine (Cl₂) are added to the mixture of U₃O₈—CsF (fromstep 1) at the rate of 3 mass parts S, 15 mass parts Cl₂ (for instance)and 36-38 mass parts U₃O₈—CsF.

At this temperature, SF₄ (produced from step 2) did not react with U₃O₈(from step 1). SF₄ has a vapor pressure of 145 PSIG at 21° C., and iscompressible as liquid in the reactor. The gas can be removed from thereactor at room temperature by passing the >99% pure SF₄ product througha 0.3 micrometer Pall's Gaskleen V filter to prevent any particulateuranium from leaving the reactor. While a description of the Batchprocess has been given, this process can be adapted for continuous flowprocess

The reaction of cesium hydroxide (CsOH) and UF₄ to produce CsF/U₃O₈ isthermodynamically favored (see Table 1), and was carried out at 600° C.to ensure dehydration of CsF produced. The reaction of potassiumhydroxide and UF₄ was previously studied by others.

TABLE 1 12 CsOH + 3 UF₄ + O₂ (g) → 12 C_(s)F + U₃O₈₊ 6 H₂O T H S G CKcal cal/K Kcal K Log(K) 100.000 −295.014 −3.790 −293.600 9.385E+171171.972 200.000 −293.680 −0.655 −293.370 3.311E+135 135.520 300.000−305.976 −25.725 −291.232 1.148E+111 111.060 400.000 −311.765 −36.289−287.337 1.980E+093 93.297 500.000 −303.628 −25.033 −284.274 2.310E+08080.364 600.000 −294.667 −14.143 −282.318 4.679E+070 70.670

Table 1 shows equilibrium constant (K) as indication of thermodynamicfeasibility of quantitative fluoride recovery from UF₄ to form cesiumfluoride (CsF).

Stoichiometric quantities of sulfur (S) and a halide such as bromine(Br₂) or chlorine (Cl₂) are added to the mixture of U₃O₈/CsF (fromstep 1) at the rate of 3 parts S, 15 parts Cl₂ (for instance) and 36-38parts U₃O₈/CsF.

The temperature-dependent thermodynamic equilibrium constant (K) data inTables 1 and 2 below show that using CsF/S/Cl₂ or CsF/S/Br₂ to produceSF₄ gas will be the most thermodynamically feasible approach, whencompared to conventional methods of KF/S/Br₂/25-70° C. (Tables 3) orNaF/S/Cl₂/92° C. (Table 4). The reactions in Tables 1 and 2 producedyields of 95-100% at 25° C./24 h or 70° C./5 h (Table 5).

TABLE 2 S + 2Cl₂ (g) + 4 CsF → SF₄ (g) + 4 CsCl T H S G C Kcal cal/KKcal K Log(K) 25.000 −72.658 −35.562 −62.055 3.102E+045 45.492 50.000−72.704 −35.709 −61.164 2.342E+041 41.370 100.000 −72.877 −36.192−59.372 5.975E+034 34.776 150.000 −73.445 −37.640 −57.517 5.119E+02929.709 200.000 −73.751 −38.325 −55.618 4.923E+025 25.692

Table 2 shows equilibrium constant (K) as indication of thermodynamicfeasibility of using the reactivity of sulfur (S) and chlorine (Cl₂) forquantitative fluoride transfer from CsF to produce SF₄ and cesiumchloride (CsCl) as byproducts.

TABLE 3 S + 2 Br₂ (g) + 4 CsF → SF₄ (g) + 4 CsBr T H S G C Kcal cal/KKcal K Log(K) 25.000 −52.338 −35.011 −41.899 5.196E+030 30.716 50.000−52.400 −35.211 −41.022 5.568E+027 27.746 100.000 −52.615 −35.814−39.251 9.790E+022 22.991 150.000 −53.225 −37.368 −37.413 2.111E+01919.325 200.000 −53.565 −38.128 −35.525 2.572E+016 16.410

Table 3 shows equilibrium constant (K) as indication of thermodynamicfeasibility of using the reactivity of sulfur (S) and chlorine (Cl₂) forquantitative fluoride transfer from CsF to produce SF₄ and cesiumchloride (CsCl) as byproducts.

TABLE 4 S + 2 Br₂ (g) + 4 KF → SF₄ (g) + 4 KBr T H S G C Kcal cal/K KcalK Log(K) 25.000 −30.923 −26.030 −23.162 9.535E+016 16.979 50.000 −30.947−26.110 −22.510 1.678E+015 15.225 100.000 −31.071 −26.452 −21.2012.618E+012 12.418 150.000 −31.563 −27.710 −19.837 1.764E+010 10.247200.000 −31.753 −28.135 −18.441 3.300E+008 8.519 Winter, R; Cook, P. W.,In A simplified and efficient bromine-facilitated SF₄-preparationmethod, J. Fluorine Chem. 2010, 131, 780-783

Table 4 shows equilibrium constant (K) and thermodynamic feasibility ofusing the reactivity of sulfur (S) and bromine (Br₂) for quantitativefluoride transfer from potassium fluoride (KF) to produce SF₄ andpotassium chloride (KCl) as byproducts.

TABLE 5 S + 2Cl₂ (g) + 4 NaF → SF₄ (g) + 4 NaCl T H S G C Kcal cal/KKcal K Log(K) 25.000 −24.197 −23.411 −17.217 4.184E+012 12.622 50.000−24.186 −23.374 −16.632 1.777E+011 11.250 100.000 −24.251 −23.547−15.465 1.143E+009 9.058 150.000 −24.696 −24.687 −14.250 2.293E+0077.360 200.000 −24.846 −25.022 −13.007 1.019E+006 6.008 1. Tullock, C.W.; Fawcett, F. S.; Smith, W. C.; Coffman, D. D., In The Chemistry ofSulfur Tetrafluoride. I. The Synthesis of Sulfur Tetrafluoride, J. Amer.Chem. Soc. 1960, 82, 539-542 2. Appel, R; Gilak, A., In Process for theproduction of sulfur tetrafluoride, U.S. Pat. No. 3,950,498, 1976 3.Oda; Y., Otouma; H., Uchida; K., Morikawa; S., Ikemura; M., In Producingsulfur tetrafluoride using amine/hydrogen fluoride complex, U.S. Pat.No. 4,372,938, 1983

Table 5 shows equilibrium constant (K) and thermodynamic feasibility ofusing the reactivity of sulfur (S) and chlorine Cl₂ for quantitativefluoride transfer from sodium fluoride (NaF) to produce SF₄ and Sodiumchloride (NaCl) as byproducts.

TABLE 6 Logarithm of equilibrium constants (log K) for the reactions ofalkaline/alkaline earth metal fluorides and chlorine for production ofSF4 as an indication of thermodynamic feasibility S + 2Cl₂ (g) + 4MF_(n) → SF₄ (g) + 4 MCl_(n)

Table 6 shows Logarithm of equilibrium constants (log K) for thereaction of alkaline/alkaline earth metal fluorides and chlorine for theproduction of SF₄ as an indication of thermodynamic feasibility.

X-Axis:

-   -   1=25° C.    -   2=50° C.    -   3=100° C.    -   4=150° C.    -   5=200° C.    -   6=N/A

Metal Temperature fluoride 25° C. 50° C. 100° C. 150° C. 200° C. NaF12.62 11.25 9.06 7.36 6.01 KF 36.03 32.77 27.55 23.55 20.37 CsF 45.4941.37 34.78 29.71 25.69 RbF 40.65 37.05 31.30 26.87 23.36 MgF₂ −41.62−38.87 −34.48 −31.14 −28.53 CaF₂ −23.20 −21.82 −19.61 −17.96 −16.68

TABLE 7 Logarithm of equilibrium constants (log K) for the reactions ofalkaline/alkaline earth metal fluorides and bromine for production ofSF₄ as an indication of thermodynamic feasibility S + 2Br₂ (g) + 4MF_(n) → SF₄ (g) + 4 MCl_(n) Metal Temperature fluoride 25° C. 50° C.100° C. 150° C. 200° C. NaF −10.81 −10.31 −9.51 −8.93 −8.48 KF 16.8915.23 12.42 10.25 8.52 CsF 30.72 27.75 22.99 19.33 16.41 RbF 23.90 21.6618.07 15.29 13.09 MgF₂ −71.27 −66.19 −58.06 −51.88 −47.02 CaF₂ −51.55−47.98 −42.28 −37.96 −34.57

Table 7 shows Logarithm of equilibrium constants (log K) for thereaction of alkaline/alkaline earth metal fluorides and bromine for theproduction of SF₄ as an indication of thermodynamic feasibility. Thesevalues are shown in graph form in FIG. 12.

Overall, determination of the feasibility of producing SF₄ from CsF/U₃O₈at room temperature has established that:

-   -   NIFUT Technology will produce high quality SF₄ at a cost        competitive process vs. conventional processes    -   Production of SOF₂, a typical byproduct in the production of        SF₄, is minimized to <2%    -   Large scale (e.g. ton scale) production of SF₄ can be carried        out in batch process, over several days    -   Since SF₄ vapor pressure is 145 PSIG at 70° F., and the gas is        condensable, it can be separated from the solid/solid reaction        phase    -   At reaction temperature, U₃O₈ (produced in step 1) does not        react with SF₄. Reaction of U₃O₈/SF₄ has been reported at 300°        C.

Example Embodiments

While certain exemplary embodiments are discussed in this disclosure, itis to be distinctly understood that the presently disclosed inventiveconcept(s) is not limited thereto but may be variously embodied topractice within the scope of the following claims. From the foregoingdescription, it will be apparent that various changes may be madewithout departing from the spirit and scope of the disclosure as definedby the following claims.

Example 1 Reaction of Uranium Tetrafluoride and Potassium Hydroxide

Step One: 35.2 g (0.112 mol) Uranium tetrafluoride (InternationalBio-Analytical Laboratories Inc, Boca Raton, Fla.) and 22.5 g (0.402mol) crushed potassium hydroxide pellets (Sigma Aldrich Co.) were placedin a 300 cc stainless steel cylinder that was then fitted into a set upillustrated in FIG. 13. A PALL Gaskleen V filter was placed in theoutlet of the continuous flow of 550 standard cubic centimeter (sccm)dry air through the cylinder reactor. The supply of dry air is carefullycontrolled through online regulator and mass flow meter. The heater ispowered on, and controlled to 600° C. for 4 h. During this period,droplets of water from the reaction were noticeable in the hose thatconnects the vent to the KOH scrubber. Any residual water was removed byvacuum of the isolated reactor, through the Gaskleen filter. Flow of dryair continued after heater power was turned off, until the temperaturedropped to 100° C. Powder X-Ray diffraction of the resulting byproductof this process showed that all UF₄ had reacted, and that U₃O₈ was theonly uranium byproduct. Based on reaction stoichiometry, 3.6 g watershould be eliminated from the reactor in a quantitative conversion, andweight loss of 7.2 g was confirmed. Thus, the reactor would contained23.3 g (0.402 mol) KF, and 31.56 g (0.034 mol) U₃O₈.

Step Two: The reactor was opened under inert atmosphere, and then 3.0 g(0.094 mol) sulfur was added to the content of the stainless steelcylinder before it was sealed (see FIG. 14). Afterwards, 14.9 g (0.210mol) chlorine gas was carefully condensed in the stainless steelcylinder reactor—and the pressure at room temperature was 39 PSIG. Thereactor was left to stand undisturbed at room temperature, andconversion to SF₄ gas was achieved after 120 h. This is confirmed bydecrease of the initial pressure from 39 PSIG to 33 PSIG, the FTIRspectrum of the gaseous content of the reactor, and gravimetric weightof cryogenically condensed product. Powder XRD analyses show that thebyproducts of this process are U₃O₈ and KCl. A determination of theuranium content of the SF₄ gas was obtained by analyzing the aliquotfrom impinging the gas into water on an inductively coupled massspectrometer (ICPMS, Perkins Elmer's ELAN-DRC II). This reaction isreported as experiment #4 in Table 8.

Example 2 Reaction of Uranium Tetrafluoride and Potassium Hydroxide

Step One: 35.2 g (0.112 mol) Uranium tetrafluoride (InternationalBio-Analytical Laboratories Inc, Boca Raton, Fla.) and 22.5 g (0.402mol) crushed potassium hydroxide pellets (Sigma Aldrich Co.) were placedin a 300 cc stainless steel cylinder that was then fitted into a set upillustrated in FIG. 13. A PALL Gaskleen V filter was placed in theoutlet of the continuous flow of 550 standard cubic centimeter (sccm)dry air through the cylinder reactor. The supply of dry air is carefullycontrolled through online regulator and mass flow meter. The heater ispowered on, and controlled to 600° C. for 4 h. During this period,droplets of water from the reaction were noticeable in the hose thatconnects the vent to the KOH scrubber. Any residual water was removed byvacuum of the isolated reactor, through the Gaskleen filter. Flow of dryair continued after heater power was turned off, until the temperaturedropped to 100° C. Powder X-Ray diffraction of the resulting byproductof this process showed that all UF₄ had reacted, and that U₃O₈ was theonly uranium byproduct. Based on reaction stoichiometry, 3.6 g watershould be eliminated from the reactor in a quantitative conversion, andweight loss of 7.2 g was confirmed. Thus, the reactor would contain 23.3g (0.402 mol) KF, and 31.56 g (0.034 mol) U₃O₈.

Step Two: The reactor was opened under inert atmosphere, and then 3.0 g(0.094 mol) sulfur was added to the content of the stainless steelcylinder before it was sealed. Afterwards, 15.0 g (0.212 mol) chlorinegas was carefully condensed into the stainless steel cylinderreactor—and the pressure at room temperature was 40 PSIG. The reactorwas heated with thermostat regulation at 80° C. for 8 h. Upon cooling,the pressure has dropped to BB PSIG, indicating that CC % conversion toSF₄ gas was achieved. Further evidence was obtained from the gravimetricweight of cryogenically condensed product, that is, 10.1 g (99.8% oftheoretical possible). Powder XRD analyses show that the byproducts ofthis process are U₃O₈ and KCl. A determination of the uranium content ofthe SF₄ gas was obtained by analyzing the aliquot from impinging the gasinto water on an inductively coupled mass spectrometer (ICPMS, PerkinsElmer's ELAN-DRC II). This reaction is reported as experiment #6 inTable 8.

Example 3 Reaction of Uranium Tetrafluoride and Cesium Hydroxide

Step One: 35.1 g (0.112 mol) Uranium tetrafluoride (InternationalBio-Analytical Laboratories, Inc, Boca Raton, Fla.) and 74.5 g (0.442mol) cesium hydroxide monohydrate (CsOH.H₂O) powder (Sigma Aldrich Co.)were placed in a 300 cc stainless steel cylinder that was then fittedinto a set up illustrated in FIG. 13. A PALL Gaskleen V filter wasplaced in the outlet of the continuous flow of 550 sccm dry air throughthe cylinder reactor. The supply of dry air is carefully controlledthrough online regulator and mass flow meter. The heater is powered on,and controlled to 600° C. for 4 h. During this period, droplets of waterfrom the reaction were noticeable in the hose that connects the vent tothe KOH scrubber. Any residual water was removed by vacuum of theisolated reactor, through the Gaskleen filter. Flow of dry air continuedafter heater power was turned off, until the temperature dropped to 100°C. X-Ray diffraction of the resulting byproduct of this process showedthat all UF₄ had reacted, and that U₃O₈ was the only uranium byproduct.Based on reaction stoichiometry, 4.7 g water should be eliminated fromthe reactor in a quantitative conversion, and weight loss of 9.2 g wasconfirmed. Thus, the reactor contained 67.14 g (0.442 mol) anhydrousCsF, and 34.70 g (0.037 mol) U₃O₈.

Step Two: The reactor was opened under inert atmosphere, and then 3.0 g(0.094 mol) sulfur was added to the content of the stainless steelcylinder before it was sealed (see FIG. 14). Afterwards, 14.9 g (0.210mol) chlorine gas was carefully condensed into the stainless steelcylinder reactor—and the pressure at room temperature was 40 PSIG. Thereactor was left to stand undisturbed at room temperature, and 100%conversion to SF₄ gas was achieved after 120 h. This is initiallyconfirmed by decrease of the initial pressure from 41 PSIG to 20 PSIG—aconfirmation that 2 mole equivalent Cl₂ is required to produce 1 moleequivalent SF₄ gas, according to the balanced stoichiometric equation.Further evidence was obtained from the FTIR spectrum of the gaseouscontent of the reactor, and gravimetric weight of cryogenicallycondensed product, that is 10 g (98.8% of theoretical possible). PowderXRD analyses show that the byproducts of this process are U₃O₈ and KCl.A determination of the uranium content of the SF₄ gas was obtained byanalyzing the aliquot from impinging the gas into water on aninductively coupled mass spectrometer (ICPMS, Perkins Elmer's ELAN-DRCII). This reaction is reported as experiment #5 in Table 8.

Example 4 Reaction of Uranium Tetrafluoride and Cesium HydroxideMonohydrate

Step One: 35.2 g (0.112 mol) Uranium tetrafluoride (InternationalBio-Analytical Laboratories, Inc, Boca Raton, Fla.) and 74.6 g (0.443mol) cesium hydroxide monohydrate (CsOH.H₂O) powder (Sigma Aldrich Co.)were placed in a 300 cc stainless steel cylinder that was then fittedinto a set up illustrated in FIG. 13. A PALL Gaskleen V filter wasplaced in the outlet of the continuous flow of 550 sccm dry air throughthe cylinder reactor. The supply of dry air is carefully controlledthrough online regulator and mass flow meter. The heater is powered on,and controlled to 600° C. for 4 h. During this period, droplets of waterfrom the reaction were noticeable in the hose that connects the vent tothe KOH scrubber. Any residual water was removed by vacuum of theisolated reactor, through the Gaskleen filter. Flow of dry air continuedafter heater power was turned off, until the temperature dropped to 100°C. X-Ray diffraction of the resulting byproduct of this process showedthat all UF₄ had reacted, and that U₃O₈ was the only uranium byproduct.Based on reaction stoichiometry, 4.7 g water should be eliminated fromthe reactor in a quantitative conversion, and weight loss of 9.7 g wasconfirmed. Cesium hydroxide is extremely hygroscopic, and the differencein amount of water lost is a reflection of moisture absorbed during thetransfer of the CsOH.H₂O into the reactor cylinder. Thus the reactorcontained 67.29 g (0.443 mol) anhydrous CsF, and 34.70 g (0.037 mol)U₃O₈.

Step Two: The reactor was opened under inert atmosphere, and then 3.0 g(0.094 mol) sulfur was added to the content of the stainless steelcylinder before it was sealed (see FIG. 14). Afterwards, 15.1 g (0.213mol) chlorine gas was carefully condensed into the stainless steelcylinder reactor—and the pressure at room temperature was 40 PSIG. Thereactor was heated with thermostat regulation at 80° C. for 8 h. Uponcooling, the pressure has dropped to 19 PSIG, indicating that 100%conversion to SF₄ gas was achieved. Further evidence was obtained fromthe gravimetric weight of cryogenically condensed product, that is, 10.1g (99.8% of theoretical possible). Powder XRD analyses show that thebyproducts of this process are U₃O₈ and KCl. A determination of theuranium content of the SF₄ gas was obtained by analyzing the aliquotfrom impinging the gas into water on an inductively coupled massspectrometer (ICPMS, Perkins Elmer's ELAN-DRC II). This reaction isreported as experiment #6 in Table 8.

TABLE 8 Production of SF₄ from UF₄ by two-step NIFUT technology anddirectly from MF_(n)

4 KF (w/U₃O₈) + S + 2 Cl₂ → SF₄ (g) + 4 KCl 4 CsF (w/U₃O₈) + S + 2 Cl₂ →SF₄ (g) + 4 CsCl Reagent composition Ex- Equiv. Equiv. peri- UF₄ M—FU₃O₈ H₂O Sulfur Halogen Process ment Added M—OH added byproduct removedadded added condition 1 — — 6.4 g — — 0.67 g 4.4 g Batch, CsF 0.021 molCl₂ RT/72 h 0.042 mol 0.062 mol 2 — — 12.5 mol — — 1.3 g 22.5 g Batch,CsF 0.041 mol Br₂ RT/72 h 0.082 mol 0.141 mol 3 35.0 g 22.5 g 23.3 g31.56 g 7.2 g 3.0 g 14.9 g Batch, 0.112 mol KOH KF 0.034 mol 0.4 mol0.094 mol Cl₂ RT/120 h 0.402 mol 0.402 mol 0.210 mol 4 35.2 g 22.5 g23.3 g 31.56 g 9.0 g 3.0 g 15.0 g Batch, 0.112 mol KOH KF 0.034 mol 0.5mol 0.094 mol Cl₂ 80° C./8 h 0.402 mol 0.402 mol 0.212 mol 5 35.1 g 74.5g 67.14 g 34.70 g 9.2 g 3.0 g 15.1 g Batch, 0.112 mol CsOH•H₂O CsF 0.037mol 0.511 mol 0.094 mol Cl₂ RT/120 h 0.442 mol 0.442 mol 0.213 mol 635.2 g 74.6 g 67.29 g 34.70 g 13.8 g 3.0 g 15.0 g Batch, 0.112 molCsOH•H₂O CsF 0.037 mol 0.767 mol 0.094 mol Cl₂ 80° C./8 h 0.443 mol0.443 mol 0.212 mol Products Ex- Analysis of products peri- SF₄M—Cl/M—Br Gas (FTIR) ment collected byproduct Solid (XRD) 1 √ SF₄, 90%,SOF₂, — 5%, Cl₂, 20%, 2 HF, 5% √ SF₄, 70%, SOF₂, — 5%, Cl₂, 20%, 3 HF,5% √ SF₄, 99%, SOF₂, U₃O₈, 0.5%, HF, 0.5% KCl 4 √ SF₄, 99%, SOF₂, U₃O₈,1%, HF, 0.5% KCl 5 √ SF₄, >99%, SOF₂, U₃O₈, 0.4%, HF, 0.5% KCl 6 √SF₄, >99%, SOF₂, U₃O₈, 0.4%, HF, 0.5% KCl ¹XRD spectra of post-reactsolid byproducts of experiments 5 and 6 are shown in FIGS. 11 and 12.²U₃O₈ prepared from step 1 was preserved intact through the processconditions of experiments 1-6. No evidence of any reaction with SF₄.

1. A method for converting depleted uranium tetrafluoride (UF₄) touranium free sulfur tetrafluoride and triuranium octaoxide (U₃O₈),comprising the steps of: heating in a first step a mixture of uraniumtetrafluoride and an alkaline compound in a first step at 350 degrees C.to 650 degrees C. in a reaction chamber for 60 minutes to 240 minutes toproduce a mixture of the respective alkaline fluoride and U₃O₈;continuously flushing said reaction chamber with dry air during heating;filtering reaction offgases to prevent particulate uranium from escapingfrom said reaction chamber; heating in a second step the mixture of therespective alkaline fluoride and U₃O₈ from said first step, combinedwith sulfur (S) and a halogen, at a temperature of 25 degrees C. to 80degrees C., for 6 hours to 120 hours; to produce sulfur tetrafluoride(SF₄) gas, and solid of the corresponding metal halide and U₃O₈ asbyproducts.
 2. The method of claim 1 in which said alkaline compoundcomprises an alkaline oxide.
 3. The method of claim 1 in which saidalkaline oxide is cesium oxide.
 4. The method of claim 2 in which saidalkaline oxide is selected from the group consisting of sodium oxide,cesium oxide, and potassium oxide.
 5. The method of claim 1 in whichsaid halogen is bromine.
 6. The method of claim 1 in which said halogenis chlorine.
 7. A method for converting depleted uranium tetrafluoride(UF₄) to uranium free sulfur tetrafluoride and triuranium octaoxide(U₃O₈), comprising the steps of: heating in a first step a mixture oftetrafluoride and cesium oxide in a first step at 350 degrees C. to 650degrees C. in a reaction chamber for 60 minutes to 240 minutes toproduce a mixture of cesium fluoride and U₃O₈; continuously flushingsaid reaction chamber with dry air during heating; filtering reactionoff gasses to prevent particulate uranium from escaping from saidreaction chamber; heating in a second step the mixture of cesiumfluoride and U₃O₈ from said first step, combined with sulfur (S) andchlorine, at a temperature of 25 degrees C. to 80 degrees C., for 6hours to 120 hours; to produce sulfur tetrafluoride (SF₄) gas, and solidbyproducts of cesium chloride (CsCl) and U₃O₈.
 8. A method forconverting depleted uranium tetrafluoride (UF₄) to uranium free sulfurtetrafluoride and triuranium octaoxide (U₃O₈), comprising the steps of:heating in a first step a mixture of uranium tetrafluoride and cesiumhydroxide in a first step at 350 degrees C. to 650 degrees C. in areaction chamber for 60 minutes to 240 minutes chamber to produce amixture of cesium fluoride and U₃O₈; continuously flushing said reactionchamber with dry air during heating; filtering reaction offgases toprevent particulate uranium from escaping from said reaction; heating ina second step the mixture of cesium fluoride and U₃O₈ from said firststep, combined with sulfur (S) and chlorine, at a temperature of 25degrees C. to 80 degrees C., for 96 hours to 120 hours; to producesulfur tetrafluoride (SF₄) gas, and solid byproducts of cesium chloride(CsCl) and U₃O₈.
 9. The method of claim 1 in which said alkalinecompound comprises an alkaline hydroxide.
 10. The method of claim 4 inwhich said alkaline hydroxide is selected from the group consisting ofSodium hydroxide, potassium hydroxide and cesium hydroxide.
 11. Themethod of claim 1 in which said halogen is selected from the groupconsisting of bromine and chlorine.
 12. The method of claim 9 in whichalkaline hydroxide is potassium hydroxide and said halogen is chlorine.13. The method of claim 9 in which alkaline hydroxide is potassiumhydroxide and said halogen is bromine.
 14. The method of claim 9 inwhich alkaline hydroxide is cesium hydroxide and said halogen isbromine.
 15. The method of claim 2 in which alkaline oxide is sodiumoxide and said halogen is bromine.
 16. The method of claim 1 in whichalkaline oxide sodium oxide and said halogen is chlorine.
 17. The methodof claim 2 in which alkaline oxide is potassium oxide and said halogenis bromine.
 18. The method of claim 1 in which alkaline oxide potassiumoxide and said halogen is chlorine.
 19. The method of claim 1 in whichsaid heating step in said first step is heated to 400 degrees C.-600degrees C.
 20. The method of claim 1 in which further comprises aheating step with stirring in step two at 80° C. or less for less than10 hours, and in which said halogen is bromine.
 21. The method of claim1 in which said heating step of step one include heating in inertatmosphere.
 22. The method of claim 1 in which said heating step in steptwo is for less than 24 hours, and further comprises a stirring step twoat 80° C. or less for less than 10 hours, and in which said halogen isbromine.
 23. The method of claim 1 in which said heating step in stepone is at room temperature for approximately 24 hours, and said heatingstep in step two is for less than 24 hours, and further comprises astirring step two at 120° C. or less for less than 10 hours, and inwhich said halogen is chlorine.
 24. The method of claim 1 which furthercomprises a cryogenic condensation step of gasses produced from steptwo.